Tool for forming the bottom of cans

ABSTRACT

A known tool for forming a container bottom, in particular the bottom of a beverage can is provided with an ejector  23  which is of sleeve-like shape and arranged between a downholder  14  and a dome  12.  The ejector  23  is biased by a spring means  26  against the activating direction of a punch  3  with a pre-tensioning force which is substantially lower than the counter force of the downholder. The spring means  26  can be formed by compression springs  27, 28  which are arranged in axial cavities formed in the front face of the ejector  23.  The ejector force can be changed by changing the compression springs or the number of compression springs.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of German Application No. 10 2010 000 235.6 filed Jan. 27, 2010.

BACKGROUND OF THE INVENTION

The invention resides in a deep-draw tool for forming the bottom of two-part cans, in particular of beverage cans but also of spray cans.

Cans are manufactured in large series production where high reliability is important. For example, DE 69802945 T2 and DE 8205933 U1 are concerned with the manufacture of cans, in particular the forming of their bottoms. The beverage cans are produced there in each case in a multi-step shaping process which among others includes a step for the manufacture of the cup shape which is called cup. The unfinished cups are first stretched in a further shaping process and subsequently their bottoms are deformed. This deformation procedure is a deep-draw process which is to be performed on the thin-walled relative delicate not yet cut can. After completion of the bottom deforming procedure the semi-finished can must be removed from the deep-draw tool and carried away. In the process it must not be stuck in the deep-draw tool nor must it be moving in an uncontrolled manner.

On this basis, it is the object of the present invention to provide a bottom forming tool for containers, in particular beverage cans.

SUMMARY OF THE INVENTION

A known tool for forming a container bottom, in particular the bottom of a beverage can is provided with an ejector 23 which is of sleeve-like shape and arranged between a downholder 14 and a dome 12. The ejector 23 is biased by a spring means 26 against the activating direction of a punch 3 with a pre-tensioning force which is substantially lower than the counter force of the downholder. The spring means 26 can be formed by compression springs 27, 28 which are arranged in axial cavities formed in the front face of the ejector 23. The ejector force can be changed by changing the compression springs or the number of compression springs.

The deep-draw tool according to the invention includes a plunger with a punch which is adapted to the desired internal shape of the can. In addition, the deep draw tool includes in a second tool part a dome which corresponds to a central concave part of the outer body shape of the can. The plunger and the dome are supported so as to be movable relative to each other wherein preferably one of the two mentioned elements, preferably, the dome is stationary. Associated with the dome is a downholder which is arranged concentrically and supported so as to be movable relative to the dome. The direction of moveability of the down holder is the same as the direction of movement of the plunger. The punch is preferably provided with a shaping surface which faces the bottom of the can. This, for example about conical, shaping surface is preferably adapted to an outer annular zone of the desired bottom shape. The down holder is supported so as to be movable preferably against the force of a draw cushion for example in the form of a pneumatic cylinder. During the deep-draw procedure it holds the bottom at an outer annular area in engagement with the punch and in this way determines or, respectively, controls to a large extent the shaping of the central bottom section.

The punch is preferably provided with aeration openings to permit the escape of air from the can when the punch moves into the semi-finished can.

In order to facilitate extraction of the semi-finished can from the deep-draw tool and to prevent its attachment to the deep draw tool, the lower tool part includes an ejector which separates the semi-finished can after completion of the bottom shaping step from the central dome and the downholder ring and brings it into a defined position. The extraction device is moved preferably by a relatively weak spring means. The movement performed, generally by the ejector is preferably greater than the stroke of the downholder. For example, the ejector and the downholder end both at an upper plane when the deep draw tool is open. When the deep draw tool is closed, however, the ejector ends preferably at the lower rim of the shaping surface of the downholder. As a result, the ejector moves with each operating stroke over a length corresponding to the sum of the downholder stroke and the ejector stroke.

Preferably, the downholder and the ejector are each annular or sleeve-like structures. They are preferably concentric to each other as well as concentric to the dome arranged in the center. The downholder and the ejector are preferably axially movable relative to each other. The spring means provided for activating the ejector is engaged preferably between the downholder and the ejector. Preferably, the spring means comprises several compression springs which are arranged in pockets of the ejector which are provided for that purpose and which are oriented axially.

BRIEF DESCRIPTION OF THE DRAWINGS

Further particulars of advantageous details of exemplary embodiments of the invention are apparent from the following drawings, in which:

FIG. 1 is a schematic representation of a machine for forming cans and bottoms of cans;

FIG. 2 is a tool utilized in the machine of FIG. 1 for forming container bottoms before the deformation of the container bottom shown in a schematic simplified longitudinal cross-sectional view;

FIG. 3 is the tool according to FIG. 2 during the transformation of the container bottom shown in a longitudinal cross-sectional view;

FIG. 4 is the tool according to FIG. 3 after completion of the transformation procedure of the container bottom with the punch retracted from the bottom part shown in a schematic longitudinal cross-sectional view; and,

FIG. 5 is the tool according to FIG. 3 after completion of the transformation procedure of the container bottom shown in a schematic longitudinal cross-sectional view.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

FIG. 1 shows a machine 1 which is used in the manufacture of cans and which performs at least the step of forming the can bottoms but, if applicable, also the stretching of the cylindrical body—so-called wall ironing. For the deformation of the bottom, the machine 1 includes a tool 2 which comprises an upper tool part 3 and a lower tool part 4. The upper tool part is in the form of a punch 3 and mounted to a plunger 5 which executes a back and forth movement as indicated by the arrow 6. The lower tool part 4 on the other hand is at least preferably stationary so that the tool 2 is opened and closed constantly in accordance with the periodic movement of the plunger 5.

The tool 2 is shown in FIGS. 2 to 4 in different operating stages. The punch 3 has for example a basic essentially cylindrical shape, wherein its lower front side faces the lower tool part 4. The punch 3 and the lower tool part 4 may be arranged side-by-side as shown in FIG. 1 or, alternatively, on top of one another or in any other orientation. The front face 7 of the punch 3 is shaped like the inner surface of the container bottom to be formed. A central concave surface area 8, as seen from the outside, is surrounded by an annular rib 9 from which an annular about conical preferably slightly concave outer surface area 10 extends up to the cylindrical outer surface 11 of the punch 3.

The lower tool part 4 includes, corresponding to the punch 3 with its shapes, in particular the shape of the front face 7, a central stationary dome 12. The dome 12 has at its side facing the front face 7, a surface area 13 whose shape corresponds essentially to the shape of the surface area 8 of the punch 3. The dome 12 is a separate element inserted into the lower tool part 4 and preferably stationarily supported therein. As illustrated in the schematic representation of FIG. 2.

Around the dome 12, an annular downholder 14 is arranged. At its side facing the punch 3 the downholder 14 is provided with a shaped surface 15, which is preferably about conical and adapted in its shape to the outer surface 10 of the punch 3. The shaped surface 15 is provided to apply during the transformation procedure a defined engagement force to an outer area 16 of the bottom 17 of the container 18 which is directed toward the punch 3 in order to control the deformation of the central area of the bottom 17. To this end, the downholder 14 is movably supported in the lower tool part 4. The direction of movement is indicated by the arrow 19 which also indicates the direction of movement of the punch 3.

In order to apply a defined force to the downholder 14, a draw cushion 20 is provided, which is, for example, in the form of a pneumatic cylinder. This is in abutment, preferably via several pressure pins 21, 22, with the front face of the downholder 14 which faces away from the punch 3.

Between the downholder 14 and the dome 12 there is preferably an annular gap whose diameter is preferably at least essentially the same as that of the rib 9. In this annular gap a sleeve like ejector 23 is arranged which is movable in the direction of the arrow 19.

As shown in FIG. 5 the ejector 23 has an upper annular front face 24 which is preferably planar and coherent. In its rest position, that is when the deep-draw tool is open, the downholder 14 and the ejector 23 are in their highest possible position. The ejector 23 then abuts an annular shoulder 25 of the downholder 14. A spring means 26, for example, in the form of a first compression spring 27, a second compression spring 28 and, if necessary additional compression springs which are not shown hold the ejector in that position. This position is shown separately in FIG. 5. The upper front face area 24 of the ejector is in this position about at the same level as the upper end 29 of the shaped surface 15 or slightly thereabove.

The compression springs 27, 28 are supported with one end on the ejector 23 and with their other end on the downholder 14, or respectively, a washer 30 mounted to the downholder 14. In FIG. 2 at the left a cavity cut into the ejector 23 for accommodating the first compression spring 27 is provided. The respective cavity for the accommodation of the second compression spring 28 is shown hidden.

The machine 1 and the tool 2 as described so far operate as follows:

First an unfinished cup-shaped interim blank for forming the container 18 is inserted into the tool 2 and the punch 3 is introduced into the interior thereof. This state is shown in FIG. 2. The still essentially flat bottom 17 of the container is disposed on the ejector 23 and/or the downholder 14. The punch 3 moves toward the lower tool part 4, that is downwardly in FIG. 2. Herewith first the ejector 23 is pushed downwardly and the compression springs 27, 28 are compressed. The spring compression force however, is substantially smaller than the force of the draw cushion 20.

Then the outer zone of the bottom 17 is seated on the shaped surface 15 whereby the outer area 16 of the container is engaged between the punch 3 and the downholder 14. With further downward movement of the punch 3, the central section of the bottom 17 is drawn over the surface 13 of the dome 12. At this point, the ejector 23 has reached its lowest possible position with regard to the downholder 14, wherein the front face 24 has reached or exceeded the lower end 32 of the shaped surface 15, shown in FIG. 5 by a dashed line 31. The drawing process is now continued in that the punch 3 is further moved downwardly until the bottom 17 is formed between the surface areas 8 and 13. As a result, the ejector 23 experiences a stroke which corresponds to the sum of the distance between the ends 29, 32 of the mold surface 15 and the stroke of the downholder 14.

Subsequently, the punch 3 is moved away from the lower tool part 4 and, as a result, out of the container 18. The downholder 23 in the process last moves the bottom 17 of the container 18 away from the surface 13. Sticking of the container 18 to the downholder 14 or respectively the shaped surface 15 is then prevented by the ejector 23. The spring means 26 pushes the container 18 at the rib formed at the bottom thereof upwardly. When the tool 1 is fully opened the container 18 is standing with its fully formed bottom 17 on the upper front surface 24 of the ejector 23 and can be carried away by a parts transport arrangement for further processing.

LIST OF REFERENCE SIGNS

1 machine

2 tool

3 upper tool part, punch

4 lower tool part

5 plunger

6 arrows

7 front face

8 surface area

9 rib

10 outer surface

11 outer plunger surface

12 dome

13 surface area

14 downholder

15 shaped surface

16 outer area of the bottom 17 of the container 18

17 bottom

18 container

19 arrow

20 draw cushion

21 pressure pin

22 pressure pin

23 ejector

24 front face

25 annular shoulder

26 spring means

27 first compression spring

28 second compression spring

29 end

30 washer

31 line

32 end 

1. A deep draw tool (2) for forming container bottoms (17) in particular bottoms of two-part beverage cans or aerosol cans, the deep draw tool (2) having open and closed positions comprising: a first tool part (3) including a punch (3) having a shape adapted to the desired inner shape of a can, a second tool part (4) including a dome (12) and an annular downholder (14) arranged concentrically with the dome (12) and supported movably relative to the dome (12) and subjected to a downholder (14) force, an ejector (23) which is annular and arranged concentrically around the dome (12), and a spring means (26) resiliently supporting the ejector (23).
 2. The deep draw tool according to claim 1, wherein the ejector (23) is biased toward the punch (3) by an ejection force which is lower than the downholder (14) force.
 3. The deep draw tool according to claim 1, wherein the ejector (23) is supported on the downholder (14) via the spring means (26).
 4. The deep draw tool according to claim 1, wherein the spring means (26) is formed by a number of compression springs (27, 28) which are arranged in axial bores of the ejector.
 5. The deep draw tool according to claim 1, wherein the downholder (14) is associated with a pneumatic cylinder (20) for generating the downholder force.
 6. The deep draw tool according to claim 1, wherein the ejector (23) has an ejector stroke, the downholder (14) has a downholder (14) stroke and the ejector (23) stroke is greater than the downholder (14) stroke.
 7. The deep draw tool according to claim 1, wherein the ejector (23) has an upper annular surface (24), the downholder (14) has an upper shaped surface (15) and the upper annular surface (24) is disposed at the upper end (29) of the shaped surface (15) when the deep draw tool (2) is the open position.
 8. The deep draw tool according to claim 7, wherein the annular surface (24) is disposed at the lower edge (32) of the shaped surface (15) when the deep-draw tool (2) is in the closed position.
 9. The deep draw tool according to claim 1, wherein the downholder (14) and the ejector (23) are in the form of concentric rings which are axially adjustable relative to each other.
 10. The deep draw tool according to claim 1, wherein the ejector (23) is arranged between the downholder (14) and the dome (12). 